There are various reasons for sensing tension in seat belt webbing. For example, it is common in a vehicle safety system to classify an occupant of a seat of a vehicle based upon a measured weight of the occupant on the seat. Protection devices of the vehicle safety system, such as an air bag or a pretensioner, are controlled based upon the occupant classification. For example, when the measured weight of the occupant on the seat is low, such as twenty pounds, the occupant classification may be a rear facing child seat. The vehicle safety system, upon the occurrence of a crash condition, may not actuate any protection devices for that vehicle seat in response to the classification of the occupant as a rear facing child seat. Accurate classification of the occupant of the seat is desirable for enhanced protection of the occupant during the occurrence of a crash condition.
The seat belt webbing may affect the measured weight of the occupant on the seat. For example, the seat belt webbing holding a rear facing child seat on the seat of a vehicle is generally locked in a position holding the rear facing child seat firmly against the seat. The downward force of the seat belt webbing on the rear facing child seat may increase the measured weight on the seat. As a result, a rear facing child seat may be incorrectly classified.
Determining the tension in the seat belt webbing enables the vehicle safety system to determine the weight attributable to the seat belt webbing so as to classify the occupant more accurately. Currently, tension sensors are sewn directly onto the seat belt webbing. If the tension sensor malfunctions or if the seat belt webbing becomes damaged, both the seat belt webbing and the tension sensor must be replaced.